The Electric Dust Storm

It’s Sunday and I’m at work. The wind outside is blowing at almost thirty mph sustained, with peak winds over forty. I’m hoping for no wildfires; today, at least, the humidity is still fairly high. It will dry out later in the week, but Lee will move away and the the winds will die down. It’s been eleven months since Texas received above-normal rainfall. The last day the state’s average temperature was below normal was probably June 22; we’ll probably break the 74 day string tomorrow.

Meanwhile, the campus golf course is just across the street from my office window. Every few minutes, the lightning alert system goes off. Sure, we’re experiencing winds from a tropical storm, but we’re on the dry side; the nearest lightning is 400 miles away and the only clouds in sight are shallow, puffy cumulus.

It was a bit challenging walking into the building, what with all the dust and debris. Soil that hasn’t received significant rain in months is easily turned into flying dust particles. I wonder: is the dust producing an electric field that is triggering the field sensors in the lightning alert system?

I recall reading the excellent book “The Worst Hard Time“, about the 1930s Dust Bowl, by Timothy Egan. To me, the most incredible part of the stories were the accounts of the massive amounts of static electricity. Sparks would fly from windmills and barb wire fences. People would drag metal chains from their cars so that the cars would remain grounded, lest enough static electricity build up that a sudden discharge to the ground would take place, shorting out a car’s electrical system.

At the time, I couldn’t conceive of a way that dust would be able to acquire such a strong electrical charge. But it turns out there are plenty of observations of lightning in dust storms or sand storms.

A research team led by Tony Shinbrot published a theory that partly describes how this would work just last year. (Strictly speaking, they’ve demonstrated and explained a phenomenon which may be the one at play in dust storms.)

Here’s the idea: tiny objects such as dust or sand in an electric field (that originates in some other way, or maybe the electric field that occurs naturally in the atmosphere is sufficient) will become polarized, as negative charges within the particle are attracted to the positive side of the electric field. I’ll let Figure 1 from the article (Pahtz, Herrmann, and Shinbrot 2010 Nat. Phys.) take it from there:

Initially (left panel) a pair of particles polarized by an external electric field collide (centre panel) to neutralize adjoining hemispheres. Once separated (right panel), the particles again become polarized by the external field. In this way, initially neutral but polarized particles gain one unit of charge following every collision. Blue denotes negative and red positive charge, as indicated by the numbers beside each hemisphere, and the arrows indicate representative particle velocities.

The net result is that the negative charges (electrons) migrate upward with each collision. Meanwhile the particles with positive charge tend to settle back toward the ground, leaving a predominantly negatively-charged cloud of particles.

Pahtz et al. worked out the physics, and showed results from numerical simulations and simple experiments that confirmed their predictions, including that there’s an ideal concentration of sand that maximizes the charges (too much or too little is no good).

So it seems that what I’m hearing out my window is not an alert of an electric field produced by a thunderstorm, but of an electric field produced by airborne dust. All the detector knows is that it has detected an electric field beyond its predefined threshold. It doesn’t know that it’s a weak field, probably strongest near the level of the detector, rather than the weak hint of a strong electric field from a thunderstorm a few miles away.

10 Responses

In rain clouds, the density difference between water and ice may account for the charge separation, with gravity’s assistance. But that wouldn’t make as much sense for dust particles of uniform density. Maybe they’re not of uniform density, size, surface texture, or composition. Perhaps there’s a relationship between one or more of those properties with their propensity to shed electrons. After particles become ionized….if they’re separated by the vortex, i.e., according to their density, it effectively separates the ions by charge.

The Worst Hard Time is a good book on the dust bowl. I lived in the Panhandle in the early fifties and saw some of the last great sandstorms, they were impressive. You can get the documentaries referenced in the book at the Harris Co library.

Gee.. you did not somehow find a way to blame AGW for all this. Guess you should get an award for that. Maybe you are the only one in “climate science”, and I use the word science very loosely, who isn’t a liar and a cheat. I think you are just playing along to keep from being fired..and who can blame you for that.

OT – Bringing AGW into the discussion (or, in other circumstances, moaning about AGW being brought into the discussion); self-satisfied sarcasm; unjustified belittling; base and unsubstantiated accusations; belief in that great big AGW conspiracy involving everyone and everything you don’t like or want to accept – what a perfect example of writing something with very little actual content or, indeed, any connection with the actual Post above.

[...] static electricity produced by the dust storms, not seen since the Dust Bowl days of the 1930s. The Electric Dust Storm | Climate Abyss | a Chron.com blog "A wise man proportions his belief to the evidence" – David Hume Reply [...]